High speed printers frequently use a rotating device to scan a writing beam across a photosensitive medium. In such devices it is important to control the writing beam to prevent corruption of the photosensitive media. Thus, it is important to know and ensure the appropriate activation of the writing beam just prior to writing of the image or information on the photosensitive medium and turning off the writing beam when the information has been completely written down. To ensure acceptable output, a mechanism is used to generate a timing pulse just prior to a detector for enabling the writing beam to excite the detector.
In prior art printers which utilize a laser beam and a rotating polygon mirror, in order to set-up this timing it is necessary to adjust several potentiometers and timing modules to accomplish the proper timing signal placement. To generate a first facet synch signal, a mono-stable multi-vibrator (one-shot) with associated RC timing network has been used which required manual intervention and the use of an oscilloscope to ensure proper placement of the one shot. It was necessary to observe the timing relationship between the polygon index signal, facet synch signal and line start signals. To generate successive facet synch pulses, a second mono-stable multi-vibrator with associated RC timing network had to be adjusted in a similar fashion. Thus, is was necessary to observe the timing relationship between line start signals and successive facet synch signals. This sequence of steps is relatively labor intensive.
The present invention replaces the labor intensive set-up sequence of the prior art and provides an automatic method for setting up and running the printing device.